This invention relates generally to an improved air-cooled battery pack with a plurality of battery cells that are used to generate motive power for vehicular and related transportation applications, and more particularly to varying the air flow amongst the individual battery cells within a battery cell module or pack such that the flow depends on each battery's position within the respective module or pack.
Various batteries, including lithium-ion, lead acid and nickel-metal hydride variants, may be configured to supplement or supplant conventional internal combustion engines (ICEs) for automotive and related transportation applications. The ability to passively store energy from stationary and portable sources, as well as from recaptured kinetic energy provided by the vehicle and its components, makes batteries (in general) and rechargeable batteries (in particular) ideal to serve as part of a propulsion system for cars, trucks, buses, motorcycles and related vehicular platforms. In one form suitable for automotive applications, the batteries are shaped as a generally thin pouched rectangular cell with edgewise-extending positive and negative voltage terminals that can be connected to a common electric current-carrying circuit. Two such cells may typically be combined into one battery unit, which in turn may be formed into even larger assemblies—including modules that in turn can be formed into a complete system known as a battery pack—to generate the desired power output. In one form of construction, the individual prismatic-shaped battery cells or their respective units are stacked along an axis that is normal to the planar faces of the cells and contained within a housing or related structure.
Battery packs are capable of generating significant amounts of excess heat during electric current charging and discharging operations. Left unchecked, this excess built-up heat may damage the cells and impact their operation. To help avoid this, cooling systems may be integrated into the battery pack. In configurations where the battery cells are stacked or arranged in a generally repeating manner, the housing or other battery structure may be formed around the cells to facilitate the delivery of air to the individual modules and cells within the battery pack. In one form, the fluid-delivery conduit may be in the form of an air manifold or plenum defined between the housing wall and the surface of the frame that holds edges of the individual cells. While such an approach has the virtue of providing a relatively unimpeded air flow path to all of the cells that are contiguous with the plenum, the potential exists for significant air flow (and concomitant temperature) non-uniformity among the individual battery cells; much of this is due to uneven pressure drops between the channels formed between adjacent cells or cooling plates as the air goes from the inlet plenum of the battery pack to the outlet plenum.
One particular form of battery pack configured with air cooling is known as the “Z-type” air-cooled battery pack. Z-type flow packs and U-type flow packs are two different arrangements of the air-cooled battery pack, where the names are in regard to the flow direction or pattern. In the Z-type flow, the cooling flows into the battery pack from the inlet such that it passes through an air manifold or plenum and over the top surface of the frame that holds the edges of the stacked cells, then down through the cooling channels that are formed between adjacent battery cells by the cells and their respective cooling plates, finally exits through the outlet by passing over the bottom surface of the frame that holds the edges of the stacked cells. By passing the air through the cooling channels, significant amounts of heat transfer may take place between the planar surfaces of the individual battery cells or cooling plate and the moving air. The inlet and outlet are located at the opposite sides of the battery pack. Conversely, in a U-type flow battery pack the inlet and outlet are typically at the same side of the battery pack. Although the uniformity of the flow rate of a Z-type flow pack can be improved by using curved upper and bottom plenums, the maximum variation of the flow rate of the individual cooling channels that define the space between adjacent battery cells or modules in the pack can still be as much as 20%. This problem is particularly significant in situations where there is a large distance between the last channel of a fluidly upstream battery module and the first channel of an adjacent downstream module; where this distance is larger than the distance between adjacent channels within the same module, the resulting pressure difference is such that the driving force (and resulting flow) in and around the first channel of each battery module is significantly reduced relative to its more closely-aligned intra-module channels.
In addition to cooling, structural rigidity considerations of the housing and cooling plenum of a conventional battery pack assembly should be addressed. While beads or related protrusions have been used to improve the stiffness of a cooling plenum used in a battery pack, the flow rate variation of individual cooling channels resulting from the use of such beaded packs is generally higher than its non-beaded counterpart. As such, the interests of a higher stiffness assembly structure may be at odds with optimum cooling flow designs.